The present invention generally relates to a recording and reproducing arrangement, and more particularly, to an optical information recording and reproducing apparatus such as an optical disc apparatus or the like having a highly reliable operation and having highly accurate recording and reproducing functions.
Recently, there has been developed an optical disc apparatus arranged for recording information on an optical disc by irradiating a laser light beam converged into a spot of light, onto the surface of the rotating optical disc, or for reproducing the information thus recorded on the disc. Since the optical disc apparatus as referred to above employs the laser light beam, the apparatus has such advantages that the track density may be made higher by more than one digit than the track density in a magnetic disc, thus making it possible to realize a memory of a large capacity. Moreover, because the construction for positioning a recording/reproducing head can be effected through non-contact by a pre-groove preliminarily cut on the disc surface, the optical disc may be readily replaced or exchanged.
However, in the known optical disc apparatus as described above, since scattering in the recording sensitivity is present among optical discs and moreover, recording and reproducing characteristics are markedly varied by temperature characteristics of laser elements, discs, etc., the recording and reproducing apparatus must be adjusted at a high accuracy. Accordingly, it has been required to provide large restrictions for a recording and reproducing characteristic allowable range of the optical discs, and a working circumstance allowable range of the recording and reproducing apparatus.
In order to overcome the disadvantages as described above, there has conventionally been proposed a practice for setting the power of the laser light beam during recording so that a fundamental wave of the reproducing signal is at the maximum power, or a practice for measuring the pulse length of the reproducing signal per each bit to obtain the recording pulse length so that the pulse length is at a predetermined length.
The above known practices for recording and reproduction still have problems in the detecting accuracy and reliability with respect to signals containing defects of discs or signals having jitters or fluctuations. Also, it is necessary for recording patterns of a special format suitable for the judging method to be adopted during actual application.
Meanwhile, there have also been developed recently various optical information recording and reproducing apparatuses arranged to converge a light beam emitted from a light source, such as a laser light source, onto a memory medium formed on a disc rotating at a constant speed for effecting recording, reproduction and/or erasing of digital information data.
In the above optical information recording and reproducing apparatuses, the reflecting light amount of the light beam, which is being projected onto the surface of the medium, reproduces signals varying in accordance to marks formed on the medium surface. For recording or erasing the signals, a light beam at a higher output than the output during reproduction is irradiated onto the medium surface. Thereby, signals are recorded or erased through the formation or elimination of the marks referred to above by the energy of light absorbed within the medium.
More specifically, recording of the information is effected by the presence or absence of marks corresponding to the amount of light incident upon a signal reproducing optical detector. As a general practice, original information data is subjected to digital modulation for band region restriction with respect to frequency characteristics of the recording/reproducing system, with the presence or absence of the marks corresponding to "1" and "0" digital values. Therefore, marks of a plurality of different lengths are required to be formed on the medium depending on the modulating system.
Conventionally, in the practice as described above, for the formation of marks of the plurality of different lengths L(n), since an accurate recording cannot be effected by merely emitting the high output beam only during the time required for movement, the beam is emitted as a high output for the time represented by (T(n)+.DELTA.T), with respect to the time T(n) necessary for the beam center to move by the length L(n) on the medium surface and the value for .DELTA.T is set to be constant irrespective of the values of n. (where n=1,2,3,. . . ,n).
However, in the conventional optical information recording and reproducing apparatus as described above, in the case where the formation of the marks is to be effected by utilizing heat generated by the light energy absorbed within the medium (referred to as a heat mode recording), heat diffusion with respect to the distribution of the converged light beam on the medium surface is brought into question. When a line recording density on the medium becomes higher, there has been such a problem that the plurality of kinds of marks as described cannot be formed by the uniform correction as described above.
Moreover, in a conventional optical disc apparatus employing, for example, in an optical magnetic disc for a recording medium, the apparatus is so arranged that, when a weak magnetic field is applied to a vertical magnetization film of the optical magnetic disc in a direction of magnetization inversion, a laser light spot is projected to locally heat the vertical magnetization film above the curie point. Thereby, the magnetic field thereat is inverted for recording of pits, while a laser light flux is projected onto the pits for detecting the rotation of the polarized face of the reflected light or transmitted light for effecting the reproduction. For the recording of the information, as illustrated in FIG. 17, the digital information of "1" and "0" is modulated into the laser driving pulse so as to turn on or off the laser light. The laser light beam having the set power during the recording above a predetermined value P.sub.0, which is necessary for the recording, is projected onto the disc being rotated at an equal speed. As a result, the recording pulse having a pulse length tw is recorded. However, in the above arrangement, because the recording is effected by the heating of the disc as described earlier, it is necessary to accurately control the on time and the power of the laser light in order to achieve the identical recording state. For this purpose, in the conventional optical disc apparatus, an adjusting knob is provided for an initial setting of the power and the recording pulse length of the recording laser light according to ambient temperatures affecting the recording quality.
Furthermore, due to the fact that the parameters affecting the recording quality of the optical disc apparatus as described above include, besides the ambient temperatures referred to above, various other factors such as variations in the recording sensitivity of the optical disc due to the temperature rise within the apparatus after turning on the power source, changes in time of the laser optical system, scattering of the recording sensitivity between the optical discs, differences in the peripheral speeds at inner and outer peripheries of the disc in the case of a disc constant speed rotating system, etc., it is difficult, in the actual application, to stably record the identical recording data with a desired reliability on the optical disc only through the initial adjustment of the recording conditions described earlier. Accordingly, there are brought about such problems as complication in the adjustment of the apparatus, loss of data interchangeability of the apparatus between the optical discs, and lowering of dependability of the apparatus.